For example, PTL 1 discloses a power transmission device for a four-wheel drive vehicle by which rotative power input from a main transmission to an input shaft is transmitted to a front-wheel drive shaft and a rear-wheel drive shaft.
This power transmission device includes a sub transmission and a center differential. The sub transmission and the center differential are each configured by a single-pinion planetary gear mechanism.
With this power transmission device, one of four operation patterns can be selected. The first operation pattern is two-wheel driving in a high-speed gear range (Hi-2WD), the second operation pattern is four-wheel driving in a high-speed gear range in a traveling condition having a differential effect between the front and rear wheels (Hi-4WD-Free), the third operation pattern is four-wheel driving in a high-speed gear range in a traveling condition not having a differential effect between the front and rear wheels (Hi-4WD-Lock), and the fourth operation pattern is four-wheel driving in a low-speed gear range in a traveling condition not having a differential effect between the front and rear wheels (Lo-4WD-Lock). This power transmission device is configured such that the switching of these operation patterns is performed using two switching mechanisms.
For example, in PTL 2, in a transfer mechanism for a four-wheel drive vehicle, a single Ravigneaux planetary gear mechanism is provided with both the functionality of a sub transmission and the functionality of a center differential.
With this transfer mechanism as well, one of four operation patterns (drive modes) that are similar to those of the power transmission device of PTL 1 can be selected. This power transmission device is configured such that the switching of these operation patterns (drive modes) is performed using three clutches and one brake.